1. Field of Invention
The present invention relates to a technique of generating image data with an imaging device, such as a digital camera. More specifically the invention pertains to a technique of generating color image data by application of a color filter array having a mosaic arrangement of fine color filters of R (red), G (green), and B (blue) corresponding to three primary colors of light.
2. Description of Related Art
With the advancement of digital techniques, images are generally processed as digital data (image data). Imaging devices such as digital cameras enable immediate output of captured images in the form of image data. The imaging device is typically equipped with an electronic image sensor consisting of small elements for converting the light intensities into electric signals. The imaging device focuses a captured image of a subject on the image sensor by means of an optical system and detects the light intensities in the individual elements as electric signals to generate image data. The light entering the optical system may be divided into three color components R, G, and B corresponding to three primary colors of light. The respective color lights of the three color components R, G, and B are focused on the image sensor, and the electric signals representing the light intensities of the respective color components are output to generate color image data.
The simplest method of focusing the respective color lights of the three color components R, G, and B, which are obtained as divisions of the light entering the optical system, on the image sensor uses a spectroscopic prism to divide the incident light into the color lights of the three color components R, G, and B and focuses the respective color lights on image sensors to generate image data with regard to the respective color components R, G, and B. This method undesirably requires the three image sensors. One extensively used technique allocates one of the R, G, and B color components to each of the elements constituting the image sensor to attain detection of the respective color components R, G, and B by one image sensor. A typical configuration of this technique provides small color filters allowing transmission of only the R component in front of the elements assigned for detection of the R component, small color filters allowing transmission of only the G component in front of the elements assigned for detection of the G component, and small color filters allowing transmission of only the B component in front of the elements assigned for detection of the B component. This configuration enables simultaneous detection of the image data of the three color components R, G, and B by one image sensor. In the technique of detecting the respective color components R, G, and B by one image sensor, each element assigned for detection of a predetermined color component (for example, the R component) is unable to detect the other color components (for example, the G component and the B component). The resulting image data accordingly has a mosaic arrangement of pixels of the R component, pixels of the G component, and pixels of the B component. Interpolation of missing color components in each pixel with color components of adjacent pixels enables generation of color image data with the settings of all the color components R, G, and B in all the pixels.
The imaging device relying on three image sensors to convert the divisional color lights of the three color components R, G, and B into electric signals and generate image data of the respective color components R, G, and B is occasionally called the ‘three image sensor’ device. The imaging device that uses only one image sensor to generate image data of a mosaic arrangement and compute the missing color components by interpolation is occasionally called the ‘single image sensor’ device. The process of interpolating the missing color components in the image data of the mosaic arrangement to generate color image data with the settings of all the color components R, G, and B is sometimes referred to as ‘demosaicking process’.
The single image sensor device requires the interpolation of the missing color components. This naturally consumes the time for interpolation and may cause the occurrence of pseudo colors due to the interpolation error. There are diverse proposed techniques with a view to preventing the occurrence of pseudo colors while minimizing an increase of the time required for interpolation. One proposed technique computes color difference components (for example, differences between the G component and the R component) in the respective pixels after computation of the missing color components, removes the pixel with the maximum color difference component and the pixel with the minimum color difference component as noise from a pixel array of a preset number of pixels including a target pixel, and recalculates the respective color components in the target pixel (see Japanese Patent Laid-Open No. 2005-167974). Another proposed technique applies low-pass filters to the color difference components computed in the respective pixels and recalculates the respective color components in the target pixel from the color difference components after removal of noise (see Japanese Patent Laid-Open No. 2005-260908).